In industry and commerce, administration offices etc. the demand of being able to code documents of various types has latterly been accentuated. The documents in question primarily are in the form of typewritten sheets and include information, which should not be accessible to everyone, for example in a company. Said demand, of course, covers written information of all imaginable types, even pictures.
In order to satisfy this demand, both an apparatus for coding the material and an apparatus for decoding the same are required.
Provided that such apparatuses are commercially available, typewritten documents, for example, can be stored in coded state and be decoded when required. Such storage can be arranged open, for example in a company, without any person being able to read the information. In such cases, however, it is very essential that not everybody in the company can utilize an apparatus for decoding all documents.
It is previously known to use a fibre-optic cable comprising a row of fibres located adjacent each other for scanning a document, where one end of the fibres are located in a certain order relative to each other, and the other end of the fibres are located in a different mutual order. A document in principle is scanned optically by one end of the fibre-optic cable while the light thus scanned is projected from the other end of the cable on a copying paper or the like. The scanning proceeds in such a manner, that the document to be scanned and, respectively, the copying paper move synchronously relative to the row or line of fibre-optic fibres, whereby the document is scanned continuously or in steps line by line.
When a document is being scanned in this way, the text or picture of the copy is distorted, i.e. coded. When thereafter the coded copy is scanned by passing the light in the other direction through the cable, the text of the original document is restored.
A coded document can be decoded when the code, which consists of the positions of the respective ends of the fibres relative to each other in a cable, is known.
It is, thus, desired to have access to a great number of different coding patterns, so that a decoding operation is extremely time-consuming and difficult, if at all practically possible to be carried out without knowledge of the code.
A further desire is that an apparatus of the kind here referred to is constructed so that different coding patterns can be utilized for different security and/or competence levels, for example of members of the staff.
The total number of coding patterns, thus, should be great. Furthermore, the switching between different coding patterns should take place repidly and unnoticeably.